Adverse reaction is every response to a medicinal product which is noxious and unintended. This includes adverse reactions arising from use of the product within or outside (including overdose, off-label use, misuse, abuse and medication errors) the terms of the marketing authorisation or from occupational exposure. The significance of public health barriers is best illustrated by the data of the European Commission, which estimates that 5% of all hospitalizations in the EU are adverse reactions . Furthermore, approximately 5% of hospitalized patients experience adverse reactions during hospitalization, and adverse reactions are the fifth leading cause of mortality among hospitalized patients. It is estimated that approximately 197.000 deaths per year in the EU are caused by side effects. It is also estimated that in the EU total direct costs due to adverse reactions amount to about 79 billion euros annually. Given that, according to the most conservative estimates, at least 30% of adverse reactions can be prevented, this means that the annual costs of preventable side effects in the EU are over 23,5 billion euros. Therefore, the European Commission estimates that even small advances in the field of drug safety can have a major and significant impact on public health and society. In Parkinson's disease, dopamine concentration in basal ganglia has been significantly reduced and pharmacological regeneration of dopaminergic activity with levodopa or dopamine agonists mitigates motor symptoms. An alternative and complementary approach is the restoration of the balance of cholinergic and dopaminergic influences on banal ganglia. The most common adverse reactions caused by levodopa are: nausea, vomiting, abdominal cramps, nightmares, orthostatic hypotension, drowsiness, dyskinesia and, especially in older and demented patients, occasional hallucinations. Side effects of direct dopamine receptor agonists are: sedation, nausea, orthostatic hypotension, psychosis. Anti- 4 cholinergic drugs have many reported adverse reactions such as dry mouth, urinary retention, constipation and visual disturbances. Because of hepatotoxicity, catechol-O-methyltransferases are rarely used.